Hm... that is an interesting question. I do not know, but I see a + next to other people's names too now that I take a look at it. Also a * on one guy. Maybe people on your friends list are +?
Finally finding about some of the bots that are flooding the users online - bytespider apparently is a huge offender here - ignores robots.txt and comes in from a ton of different IPs
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.